function action(num = 200) {
    console.log(num)
}
action(0) // 0
action() //200
action(300) //300
function show({a=1,b=2}={}) {
    console.log(a,b)
}
show() //1 2
show(3) //1 2
show({a:3}) //3 2
show({a:3,b:4}) //3 4
function fn(a,b,...c) {
	console.log(a,b,c)
}
fn(1,2,3,4,5)  //1 2 [ 3, 4, 5 ]
fn(1,2) //1 2 []
fn(1,2,3) //1 2 [ 3 ]
fn(1)  //1 undefined []
function fn2(...a) {
	console.log(a,...a)
}
fn2(1) //[ 1 ] 1
fn2(1,2) //[ 1, 2 ] 1 2